Spiral gas-solids contact apparatus and method

ABSTRACT

The invention is directed to apparatus and methods for contacting gas and solids in the manufacture of edibles, and particularly in connection with coating edible particulate solids. A drum is positioned around an inner tube so that an annular space is defined between the drum and the tube. A rotatable spiral element defines a gas pathway in the annular space, such that rotation of the spiral pushes particulate solids through the drum while the solids are contacted with gas in the annular space.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to apparatus and methods for contacting gasand solids in the manufacture of edibles, and may be used for drying,drying combined with coating, heating, cooling, and cooling combinedwith coating.

2. Description of the Related Art

Application of a sugar layer to the exterior of a solid particle is acommon practice in the confectionery and pharmaceutical arts. Thecommonly practiced batch panning process, in which sugar syrup is addedto the solids shot by shot, is highly capital and labor-intensive, and asignificant amount of sugar is carried away in the course of drying.There would be many practical advantages if such coating processes couldbe practiced on a continuous basis. However, apparatus for conductingthis type of coating on a continuous basis have not gained widespreadacceptance because they have not yielded acceptable product quality.

U.S. Pat. Nos. 6,364,948 and 6,689,417, which are owned by the assigneeherein, are directed to methods and apparatus for batch coating and/ordrying (including methods for making sugar shell coated products) inwhich particles are placed in a bed and displaced in the x, y and zdirections by vibrating the bed so that the particles follow a dominantpath or direction. Drying air is provided tangentially to the bed.

U.S. Pat. No. 6,638,550, owned by the assignee herein, is directed tomethods for forming a shell coating on a mass of confectionery centers.The process may utilize a rotatable drum in which a current of dryinggas is provided having a controlled moisture content.

U.S. Pat. No. 6,960,361, owned by the assignee herein, is directed to apanning apparatus for coating a plurality of center materials. Thepanning drum incorporates a partition, dividing the drum into aplurality of coating vessels.

Published International Application WO 99/26484 teaches an apparatus forbatch coating chewing gum or other edible materials. The apparatuscomprises a rotating drum having angled baffles on the inside. Liquidcoating material is provided through an internal pipe running along theaxis of the drum, and drying air is provided through a plurality of airdistribution chambers arranged around the periphery of the drum. Airsupply and removal conduits are provided so that drying air travelsaxially in the drum.

U.S. Pat. No. 6,365,203 B2 and No. 7,022,353 B2 teach a method andapparatus for continuous coating of gum materials. The coating materialmay be a hardenable sugar solution. The apparatus comprises a rotatingdrum which is angled with respect to the horizontal so that the ediblepieces move through the drum by the force of gravity. The residence timeis shortened or increased by raising or lowering the angle of the drum.Liquid coating material is fed to the drum through a central conduitalong the principle axis of the drum, while heated drying air ispreferably introduced through perforations in the side walls of thedrum, to provide a uniform flow of drying air in the drum.

U.S. Pat. No. 5,520,457 and EP 0 192 012 teach coating apparatus andmethods for coating particulate solids in which a rotating spiral brushis used to push material through a drum, which may also rotate. Theseapparatus and methods do not contemplate a system wherein a source ofgas is provided to a substantially closed gas pathway defined by aspiral element.

WO 2005/011398 discloses a method for continuously coating cores in adragee making process, which comprises transporting the cores through arotating drum with a screw-like conveyor.

None of the foregoing disclosures effectively makes use of a closed gaspath for contacting solids with gas in a controlled, continuous manner.A significant problem with prior art methods and apparatus for coatingparticulate solids concerns the handling of dust formed by the tumblingaction of the solids. The dust becomes airborne and may damage humiditycontrol systems. Expensive dust filtration equipment may be required,increasing both the complexity of the process and maintenance costs.This problem may be solved according to the present invention bydirecting the flow of process gas to ensure that dust formed by tumblingthe solids is adhered to the solids before the solids are dischargedfrom the apparatus.

SUMMARY OF THE INVENTION

The present invention is directed to methods and apparatus for effectinggas-solids contact in the manufacture of edibles, and can be adapted forcoating particulate edible materials with flowable coating material anddrying the coating on the particles, such as in the coating of chocolatecenters with sugar syrup and drying to form a sugar shell in theproduction of M&M's® Milk Chocolate Candies. These methods and apparatusmay also be used in connection with coating particulate edible materialswith flowable coating material and solidifying the coating on theparticles, such as in the coating of peanuts with liquid chocolate inthe production of M&M's® Peanut Chocolate Candies. Alternatively, thesemethods and apparatus may be used for heating, e.g., cooking androasting, and cooling of particulate edible materials.

Particulate edible materials that may be processed with the methods andapparatus of the invention include, without limitation, confectionery,including chocolate, caramel, nougat, gummies, pressed candies, and hardcandies. As used herein, “chocolate” includes chocolate meeting theStandards of Identity (SOI) for chocolate defined by the Food and DrugAdministration, as well as non-SOI chocolate. Edible materials alsoincludes, without limitation, wafers, crackers, biscuits, cookies,granola, rice, grains, legumes, cocoa beans, coffee beans, nuts, freshand dried fruits, fresh and dried vegetables, dairy snacks, cheese, petfood, and pet treats. Edible materials also includes pharmaceuticals,including without limitation, tablets, caplets, agglomerations, andgel-caps.

In one aspect, the invention is a gas-solids contact apparatuscomprising a drum having an interior wall concentric with an inner tubeand defining an annular space between the drum and the inner tube. Gasis supplied from a source of gas to the annular space at a gas entryzone, and particulate solids are introduced to the drum at a solidsentry point. At least one spiral element (sometimes referred to hereinsimply as the “spiral”) in the annular space defines a gas pathway inthe annular space. Rotary motion is imparted to the spiral (with amotor, for example) to move the solids through the drum.

The gas-solids contact apparatus may be combined with a coating materialdispenser for adding coating material, which is then dried or solidifiedon the surface of the solids as the solids progress through the drum.

In particularly preferred embodiments, especially where the apparatus isused for coating confectionery center materials with a sugar syrup anddrying the coating to form a shell, the apparatus includes a drumrotatable around a horizontal longitudinal axis, and the gas entry zoneand the solids entry point are proximate opposite ends of the drum withrespect to the longitudinal axis, so that the gas travels along a gaspathway substantially countercurrently with respect to the solidstraveling through the drum. This has the advantage that the process gascarries dust formed from the tumbling action of the solids in thedirection of the wetted solids, so that the airborne dust adheres to thesolids. Countercurrent, in this context, means that the gas entry zoneand the solids entry point are generally at opposite sides of the drum.

In another aspect, the invention is a method of coating a plurality ofedible particulate solids. A drum is provided having an interior wallconcentric with an inner tube so that an annular space is definedbetween the inner tube and the drum. A spiral element is positioned inthe annular space defining a gas pathway in the annular space, and isrotatable to move particulate solids through the drum. The methodinvolves introducing particulate solids into the drum, applying acoating material to the particulate solids to form coated particulatesolids, and imparting rotary motion to the spiral element to causemovement of the coated particulate solids through the drum. At the sametime, gas is flowed from a gas entry zone along the gas pathway definedby the spiral element to dry or solidify the coating material on theparticulate solids. After traveling through the drum, the coatedparticulate solids are discharged from the drum.

In another aspect, the invention is a method of contacting gas andparticulate solids in the manufacture of edible products. A drum isprovided as described above and particulate solids are introduced intothe drum at a solids entry point. The spiral element is rotated so thatthe particulate solids are pushed through the drum in the annular space.Gas is flowed from a source of gas into the annular space along the gaspathway defined by the spiral element, and solid particulates aredischarged from the drum. In this aspect of the invention, the methodmay used to heat or cool edibles without coating them.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a side cutaway view of an apparatus according to theinvention.

FIG. 1B is a side cutaway view of an apparatus according to theinvention in an embodiment where gas is supplied inside the inner tubeof the apparatus.

FIG. 2 is a perspective view of a drum and spiral element in theapparatus of FIG. 1A, with the inner tube removed, wherein the spiralelement is attached to (and rotates with) the drum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In an embodiment depicted in FIG. 1A, drum 10 is rotatable as indicatedat 12. An annular space 30 is defined between interior wall 14 of thedrum and the inner tube 20. In the embodiment shown, spiral element 110extends from the interior wall of the drum into the annular space 30,and motor 22 imparts rotary motion to the drum and the attached spiralelement, while the inner tube 20 remains stationary with respect to thespiral and drum.

Alternatively, a motor may be provided to impart rotary motion to thespiral 110, independently of the rotation of the drum 10. For example,the drum 10 may remain stationary, while the spiral extends from, androtates with, inner tube 20. The rotation of the spiral primarilyaffects residence time of the solid particles in the drum, and therotation of the drum primarily affects the speed of mixing of theparticles.

Mixing ribs 19 are spaced on the interior surface of the drum, forexample at 10°, 15° or 20° intervals, to reduce slippage of the producton the surface, and promote mixing. If the drum moves independently ofthe spiral, a mixing element may be attached to the edge of spiral 110to perform a similar function. The height of the ribs on the interiorsurface of the drum may be determined by trial and error based on thesize of the drum, the size of the solid particles, the spacing of theturns of the spiral and other considerations. In general, the mixingribs have a height at least equal to the particle diameter. Inembodiments, the ribs have a height in a range of about 0.1 cm to about5.0 cm.

The spiral 110 extends radially into the annular space, positioned sothat particulate solids are pushed through the drum as the spiral turns,in the manner of a screw. Typically, the drum is a regular cylinder,horizontally arranged, and the spiral is oriented on the same axis asthe drum, occupying the entire annular space, as shown in FIG. 2. Thedistance between each turn of the spiral is referred to as the pitch. Inthe embodiment shown in FIG. 2, spiral 110 extends radially into theannular space 30 from the interior wall of the drum. Within the scope ofthe invention, the distance between turns of the spiral (the “pitch”)can vary along the length of the spiral element, and the radius of turnsof the spiral can vary.

Appropriate journaling 18 and air seals are provided, in a manner knownto one of ordinary skill in the art, to allow for relative rotation ofthe drum, the inner tube, and/or the spiral element with respect to thestationary entrance shroud 24 and exit shroud 16.

In the apparatus, the solids are contacted only with the gas from gassupply 90 and not with ambient air from outside the drum, although someminimal contact may be unavoidable. Thus, the system is said to be“substantially sealed” to outside air, even though the system is nothermetically sealed. In a preferred embodiment, the system is “closed,”in that gas withdrawn from the drum is conditioned at a gas conditioningplant (not shown) and returned to the gas entry zone. Alternatively, itmay be possible to operate an “open” system, such that gas from the gassupply contacts the edible materials in the drum and thereafter isvented to the atmosphere.

The spiral element defines a gas pathway shown by arrows 92. The spiralelement is configured in the annular space so that gas does not travelaxially through the annular space except along the spiral path shown.There may be some escape of air, but this should be negligible.

In FIG. 1A, drum 10 has a substantially cylindrical interior wallrotatable around a horizontal longitudinal axis. The gas entry zone 140and the solids entry point 130 are proximate opposite ends of the drumwith respect to the longitudinal axis so that the movement of gas fromgas supply 90 to gas exit 94 is substantially countercurrent to themovement of solids through the drum. Countercurrent operation ispreferable in an application such as coating confectionery centers withliquid syrup combined with drying the liquid syrup to form a sugarshell, because the drying air having the lowest humidity is expected tocontact the solids toward the end of the processing, where more intensedrying is required. Also, as dust from the particulate solids and driedcoating material becomes suspended in the gas, dust-laden gas is carriedtoward the solids entry point where the coating on the solids is moreliquid, such that the gas is contacted with liquid coating material anddust is removed from the gas by adherence to the particles. A screen 120or other suitable partition with apertures prevents particles from beingentrained by the gas into the entrance shroud 24.

In other embodiments, the drum is rotatable around a horizontallongitudinal axis, as shown in FIG. 1A, but the gas entry zone and thesolids entry point are positioned proximate the same end of the drumwith respect to the longitudinal axis, so that the gas proceeds along apathway in substantially co-current fashion with respect to the movementof solids through the drum. The co-current arrangement is preferablewhen the coating material is expected to require rapid initial coolingto solidify onto the particulate solids, such as a liquid chocolatecoating material solidified on an edible center material. Co-current, inthis context, means that the gas entry zone is generally on the sameside of the drum as the solids entry point.

Where chocolate is used as a coating material, it may be desirable toutilize a co-current arrangement further to promote the formation ofstable polymorphic forms of the chocolate as it cools. This arrangementmay prevent exposure of the chocolate to air that is too cold, whileexposing the chocolate coating to slightly warmer air where thechocolate is required to recrystallize.

In embodiments, the inner tube 20 is a closed, air-impermeable volume.In this case, gas supply 90 is introduced directly into the shroud 16,and then into annular space 30, in the direction of the gas pathwayindicated by arrows 92.

As shown in FIG. 1B, it is also possible to provide an opening 96 in theinner tube through which gas is supplied from gas supply 90. Apertures98 in the inner tube 20 permit flow of a gas from the inner tube intothe annular space between the drum and the inner tube. An additionalsource of gas 91 (which may be the same as or different from gas supply90) may be provided directly to the annular space. By adding gas frominner tube 20 into the annular space 30 along the length of the drum, itis possible to control gas temperature and condition at different pointsin the process. For example, warmer air could be added toward the solidsentry point to provide enhanced evaporation where the coated particulatesolids are wetter. Arrows 93, 95 and 97 show an increase in gas massflow rate along the length of the drum due to addition of gas from theinner tube 20 at different points along the drum. As in the embodimentdepicted in FIG. 1A, the gas pathway is “closed” in the sense that thegas can only move through the drum along the path defined by the spiralelement 110.

Once the gas exits inner tube 20, it follows the closed spiral pathwayto gas exit 94. The apertures 98 can be placed where desired along thelength of the inner tube 20. For example the apertures may be placed atspecific points, rather than along the entire length of the tube asshown in FIG. 1B.

In FIG. 1B, the inner tube 20 is shown capable of rotating in adirection 112 opposite to the direction of rotation 12 of the drum 10.The inner tube 20 may also rotate in the same direction as the drum 10,or the inner tube 20 may remain stationary. In FIG. 1B, the spiral 110is shown attached to and extending radially outward from the inner tube20.

In the embodiment shown in FIG. 1A, wherein gas-solids contact iscountercurrent, the length of the inner tube defines a gas-solidscontact zone within the drum. A solids entry zone extends from a pointwhere the inner tube terminates to the solids entry point 130, wheresolids are deposited in the drum (in FIG. 1A, this is just to the leftof screen 120). A gas entry zone 140 extends from the gas supply 90 tothe beginning of inner tube 20. Because the inner tube 20 typically doesnot extend the entire length of the drum, the gas has higher velocity inthe gas-solids contact zone than in the solids entry zone because of thesmaller cross-sectional area through which the gas flows along thatlength.

Depending on the application, the size of the drum relative to the innertube, and the desired flow rate of the gas in different parts of theapparatus, the solids entry zone may have zero length (in the case wheresolids are deposited on the inner tube), or the solids entry zone maycomprise from zero up to about 50 percent of the length of the drum.This length may be in a range of about 2 percent to about 30 percent ofthe length of the drum, and preferably is in a range of about 5 percentto about 15 percent of the length of the drum. In embodiments, thesolids entry zone preferably constitutes about one to about two spiralpitch-lengths from where the solids enter the drum. The optimal lengthof the solids entry zone will depend on the amount of mixing required(in the solids entry zone, where the gas velocity is lower) compared tothe amount of drying required (in the gas-solids contact zone, where thegas velocity is higher).

In the embodiment shown, particulate solids are added at solids entrypoint 130 to form a bed of particles 36 in the drum. The solidsdispenser for dispensing particulate solids to the drum may comprisehopper 50, and inlet tube 60. A flow metering device, such as a screwfeeder, belt feeder or similar device known to one of ordinary skill,may be used to meter a desired quantity of particulate solids. A rotaryair lock 54 allows the controlled entry of product into the apparatuswhile minimizing excessive passage of air. A similar rotary air lock 84at a solids exit 70 performs a similar function. A flowable coatingmaterial dispenser 56 dispenses a flowable coating material, such asliquid sugar syrup, in the inlet tube 60. The inlet tube 60 has asmaller diameter than the drum so that flowable coating materialdispensed from flowable coating material dispenser 56 can be intimatelycontacted with the particulate solids before the particles areintroduced into the drum. Thus, liquid syrup dribbled on particles inthe inlet tube 60 is roughly distributed on a piece-to-piece basis ontothe majority of particles before they reach the solids entry point 130.This initial piece-to-piece spreading in the inlet tube allows for morerapid and even spreading of the syrup onto all particle surfaces in thesolids entry zone during the tumbling in the drum. The addition of syrupin the inlet tube also avoids syrup dripping directly on the spiral.

If the flowable coating material is a coating material crystallizableupon cooling, such as a chocolate or other fat-based material, atemperature-controlled coating material dispenser may be used (usingthermal jacketing or the like) to keep the crystallizable coatingmaterial in a flowable state as the coating material is applied to theparticulate solids.

In some instances, it may be desirable to use a plurality of coatingmaterial dispensers at a plurality of points along the drum. Dependingon the coating material, it may be desirable to minimize the contact ofthe coating material with the spiral. Accordingly, a dispenser indexedto the pitch of the spiral, or a plurality of dispensers, accessing theannular space through the inner tube, may be provided.

For example, chocolate coating of solid particulates may be accomplishedin the apparatus by a multiple point chocolate addition system (notshown). A chocolate addition nozzle is located midway between adjacentturns of the spiral along the length of the drum and passing through aspecific point of the inner tube. Location of the nozzle midway betweenadjacent turns of the spiral is desirable to prevent chocolate drippingon the spiral where it could build up. The number of nozzles may beapproximately equal to the number of turns of the spiral along thelength of the drum, although preferably, chocolate should not be addedin the last several pitch lengths of the drum in order to allow thechocolate to fully solidify onto the particulate solids before exitingthe drum. The nozzles may be connected to a chocolate delivery pipemounted along the centerline of the drum, which pipe may be suppliedthrough a rotary union connected to the end of the drum shroud. Asynchronization system may allow chocolate to be pumped on the particleswhen the nozzles are located above the particles tumbling in the drum.With this arrangement, chocolate is only added during the portion of thedrum rotation when the nozzles are located approximately above theparticles.

As another example, a nozzle arrangement is also possible wherechocolate is added to the particles during the majority of the drumrotation. A spiral slot is cut into the inner tube for each nozzle topass through. A single nozzle slot occupies slightly less than 360degrees of drum rotation and is located midway between adjacent turns ofthe spiral. A synchronized motor and positioning system may be designedto allow the nozzles to maintain their bottom centerline location whileadding chocolate for slightly less than 360 degrees of drum rotation. Areciprocating system may be provided to stop the chocolate flow and movethe nozzles back to their starting positions at a high rate of speedcorrelating to a drum rotation of about 10 degrees. The nozzles may thenrepeat the chocolate addition process. A louver, rubber seal, or brusharrangement is possible to cover all sections of the slot, except wherethe nozzle is passing at that point of rotation, to prevent bypass ofair.

Upon motion being imparted to the spiral, the particulate solids arepushed through the drum to a solids exit area 70. The length anddiameter of the drum are sized to give the desired residence time of theparticulates in the drum, considering the drum diameter, pitch of theturns of the spiral, depth of the bed of particulates formed in thedrum, and the speed of revolution of the drum. A larger drum ispreferable when more tumbling energy needs to be imparted to theparticles, and where larger flow rates are required. Process economicswill dictate whether a plurality of drums arranged in series ispreferable to a single, larger drum. For typical applications in thefood industry, with particulates in a range of 1 mm to about 100 mm, itis expected that a suitable drum diameter is in a range of about 0.01 mto about 20 m, preferably in a range of about 0.1 m to about 5 m. Thelength of the drum preferably is in a range of about 0.1 m to about 10m.

Typically, the spiral rotates with the drum and the drum is generallycapable of rotating at a speed of about 0.1 RPM to about 20 RPM.Preferably, for most gas-solids contact operations, including coating, aspeed of 1 RPM to about 5 RPM is satisfactory. In most applications, formost reasonable apparatus configurations, this speed of rotation yieldsa solids flow rate of about 0.1 kg/min to about 100 kg/min. Theresidence time in the drum for most coating and/or gas-solids contactoperations is in a range of about 1 minute to about 60 minutes.

If desired, coated particulate solids exiting the drum can be returnedvia conveyors back to the inlet end of the machine and introduced whilestopping the introduction of the uncoated product so that additionalcoating material can be added on the surface.

The spacing between adjacent turns of the spiral must be at least about3 times as large as the width of the individual particulates to preventclogging of the particulates in the turns of the spiral. Morepreferably, the pitch of a spiral element is in a range of about 1 cm toabout 50 cm.

In the embodiment shown in FIG. 2, the inner tube is designed so that itcan be removed for cleaning and maintenance of the interior of the drum,and for installation of instruments and/or coating material applicationequipment and to allow the required drying air flow. It is expected thatthe diameter of the inner tube will be in a range of about 0.001 m toabout 10 m. In embodiments, the inner tube extends from a first end ofthe drum and does not extend the entire length of the drum, as describedabove. The length of the inner tube defines a gas-solids contact zone.Thus, in FIG. 1A, from the point where the inner tube 20 terminates tothe point where solids drop into the drum at solids entry point 130, isthe solids entry zone. From the gas supply 90 to the beginning of theinner tube 20 is the gas entry zone. Preferably (at least in theembodiments wherein the apparatus is used for coating particulates anddrying), particulate solids can be fed to the drum and coated withflowable coating material in the solids entry zone before beingcontacted with significant drying air flow. Where the apparatus is usedfor coating chocolate particulates with a sugar solution followed bydrying, a ten-foot-long drum with a six-foot-long inner tube has beenfound to be operable.

If chocolate, a chocolate-like substance, fat-based material (such ascocoa butter) or other coating material crystallizable upon cooling isused, temperature control may be provided to the coating materialdispenser to keep the material in a flowable state. This may include,for example, thermal jacketing provided with a heat exchange fluid,electrical heaters, and the like.

While in some instances it may be possible to feed enough particulatesolids into the drum to completely fill the annular space, in mostcases, it is more desirable to have a particle bed 36 formed, such thatthere is a distance between the top of the particle bed 36 and the innertube 20, as shown in FIG. 1A. This distance is referred to as theparticle to inner tube annulus. The annulus size is primarily chosen toachieve the desired air flow and velocity, which impacts both theeffective heat and mass transfer rate and the overall energy balancebetween air and particulates. Generally, the depth of the particle bedat the deepest point is in a range of about 10% to about 90% of thedistance between the interior wall of the drum and the inner tube.Therefore, the particle to inner tube annulus is generally in a range ofabout 90% to about 10% of the distance between the interior wall of thedrum and the inner tube. In the method practiced according to theinvention, it is preferred to maintain a predetermined minimum particleto inner tube annulus.

The gas used in the present invention, whether for drying, cooling orheating, is typically air which has been conditioned to remove dust andto have a specified moisture content (dew point) and temperature. Gasmay be removed from the drum at gas exit 94 and conditioned with an airconditioner or “handler” (not shown). The conditioned gas is thenrecycled to the gas supply 90. The properties of the gas will depend onthe process requirements, but typically the dew point of the gas supplyis in a range of about −40° C. to about 10° C., preferably in a range ofabout −20° C. to about 10° C. The flow rate of gas is generally in arange of about 0.01 cubic meters per second to about 100 cubic metersper second, and the temperature is in a range of about −10° C. to about250° C. The apparatus operates at about atmospheric pressure, though theactual pressure may be slightly higher or lower.

EXAMPLES Example 1

In this Example, an apparatus having the configuration shown in FIG. 1Ais used for continuously coating sugar syrup on confectionery centers.The drum is 1.23 meters in diameter with a working distance between thespiral flights of 15 cm. The length of the drum is 3 meters. Thediameter of the closed, air-impermeable inner tube is 61 cm, and thelength is about 2.44 meters. An air conditioning system is connected tothe system in order to supply air at the desired flow rate, temperature,and humidity. Air is flowed along a spiral pathway countercurrently tothe movement of the solids.

The coating drum is equilibrated to 20° C. by storage in a 20° C. room.The drum speed is set to 2 RPM. Starting materials consisting oflentil-shaped chocolate pieces (also called “centers”) at 20° C. andweighing 0.6 grams each are introduced into one end of the drum at aflow rate of 500 kg/hr. Coating syrup consisting of 66.7 wt % sucroseand 33.3 wt % water is pumped onto the entering pieces at a flow rate of7.5 kg/hr at the same end of the drum. Drying air is pumped into thedrum countercurrently to the product flow at the opposite end of thedrum at a flow rate of 15 cubic meters/min. The air flow is increased toobtain more dry product or decreased to leave more moisture in theproduct. The temperature of the air is 50° C. with a dew point of −10°C. After approximately 10 minutes residence time, the coated productemerges from the system. Each coated product piece increases in weightby approximately 1 wt % on each passage through the system. The weightloss between added material and exit material is from water removed bythe drying air.

The flow of solids in the apparatus approximates plug flow. Therefore,after the first coated product emerges, the bare centers input can bestopped. The coated product can be recycled back to the solids entryzone of the drum as many times as needed to obtain the desiredconsistent number of shell layers on each piece. In the present example,the coating time is about 250 minutes. This results in each piece havingpassed through the spiral coater approximately 22 times and having closeto 20% by weight hard sugar shell added. This coating process requires a21 kg surge hopper in the recycle loop to accept the increase inmass/volume of the product as sugar shell is added.

If desired, the sugar coating process could alternatively beaccomplished using 22 drums in series so that recycle would not benecessary. The operating conditions of each drum in the series wouldneed to be adjusted to account for the greater mass input as the productprogresses downstream. The first drum in the series would mostpreferably be operated as described above.

Example 2

An apparatus substantially similar to that depicted in FIG. 1A with thesame physical geometry as described in Example 1 is used to performcontinuous baking of peanut crackers. The starting material is 80 wt %oil-roasted peanuts coated with a 20 wt % layer of firm dough at 20° C.The dough composition on a dry weight basis is approximately 38% cornflour, 38% corn starch, 17% water, 3% 43DE corn syrup solids, 2% gumarabic, and 2% sucrose. No coating material is added inside theapparatus. In order to bake the products, 30 cubic meters per minute ofhot air (200° C.) having a dew point of 10° C. is pumped into thesystem. The speed of the drum is set to 2 RPM. The movement of solids inthe apparatus is adjusted in order to obtain product with an exittemperature of 120° C. The solids inlet flow rate is reduced if the exitproduct temperature falls below 120° C. Conversely, the product flowrate is increased if the exit product temperature exceeds 120° C. Bakedpeanut crackers are withdrawn from the continuous apparatus ready foruse or further processing. As one pass through the system delivers thedesired end product there is no need for recycle.

Example 3

An apparatus substantially similar to that depicted in FIG. 1A with thesame physical geometry as described in Example 1 is used to performcontinuous coating of oil-roasted peanuts with chocolate. The primarydifference is that, in place of the syrup addition tube, a reciprocatingchocolate manifold is used to apply chocolate to the peanuts in each ofthe zones of the spiral. The coating drum is equilibrated to 5° C. bystorage in a 5° C. room. The drum speed is set to 4 RPM. Startingmaterials consisting of oil-roasted peanuts (also called “centers”)weighing 2 grams each at 15° C. are introduced into the drum at a flowrate of 1000 kg/hr. SOI chocolate is sprayed onto the peanuts at 125kg/hr uniformly along the first two-thirds of the drum length. Coolingair at 5° C. is pumped into the drum at a flow rate of 50 cubicmeters/min co-current to the product flow at the same end of the machinewhere the peanuts enter. The air flow is increased to obtain colderproduct or decreased to allow more smoothing of the product. Afterapproximately 5 minutes residence time, the coated product emerges fromthe system still at 15° C. or slightly higher if more smoothing isdesired. Each coated product piece increases in weight by approximately11.1 wt % on each passage through the system.

The flow of solids in the apparatus approximates plug flow. Therefore,after the first coated product emerges, the bare peanuts input can bestopped. The coated product can be recycled back to the solids entryzone of the drum as many times as needed to obtain the desired weightpercent chocolate shell. In the present Example, the coating time isabout 80 minutes. This results in each peanut center having passedthrough the spiral coater approximately 11 times. The final productcomposition is 2 parts chocolate for every 1 part peanut. This chocolatecoating process requires an approximately 167 kg surge hopper in therecycle loop to accept the increase in mass of the product as chocolateis added.

If desired, the same chocolate coating process could alternatively beaccomplished using 11 drums in series. The size of each drum in theseries may need to increase as the product progresses downstream inorder to account for the large increase in volume of the product. Thepotential exists that the process conditions or a combination of drumgeometry and process conditions could also be adjusted as the productprogresses downstream.

The foregoing examples and detailed description are for the purposes ofillustration only and are not to be deemed limiting of the invention,which is defined by the appended claims.

1. A gas-solids contact apparatus for processing edibles, comprising: adrum having an interior wall concentric with an inner tube and definingan annular space between the drum and the inner tube; a source of gassupplying gas to the annular space at a gas entry zone; a solids entrypoint for introducing particulate solids to the drum; at least onerotatable spiral element in the annular space defining a gas pathway inthe annular space; wherein the apparatus is adapted to impart rotarymotion to the spiral element to move the solids through the drum.
 2. Thegas-solids contact apparatus of claim 1, wherein the inner tube is aclosed, air-impermeable volume.
 3. The gas-solids contact apparatus ofclaim 1, wherein the inner tube comprises apertures permitting flow of agas from the source of gas into the inner tube and from the inner tubeinto the annular space between the drum and the inner tube.
 4. Theapparatus of claim 1, wherein the spiral element is attached to, andextends radially inward from, the interior wall of the drum and rotateswith the drum.
 5. The apparatus of claim 1, wherein the spiral elementis attached to, and extends radially outward from, the inner tube androtates with the inner tube.
 6. The apparatus of claim 1, furthercomprising a coating material dispenser.
 7. The apparatus of claim 1,further comprising: a gas removal zone where gas is removed from thedrum, and a gas conditioning system adapted to filter the gas removedfrom the drum, to condition the gas to a predetermined temperature andrelative humidity, and to redirect the conditioned gas to the drum. 8.The apparatus of claim 1, wherein: the drum is rotatable around ahorizontal longitudinal axis; and the gas entry zone and the solidsentry point are proximate opposite ends of the drum with respect to thelongitudinal axis so that the flow of gas along the gas pathway issubstantially countercurrent to the movement of the solids in the drum.9. The apparatus of claim 1, wherein: the drum is rotatable around ahorizontal longitudinal axis; and the gas entry zone and the solidsentry point are proximate the same end of the drum with respect to thelongitudinal axis, so that the flow of gas along the gas pathway issubstantially co-current with the movement of the solids in the drum.10. The apparatus of claim 8, wherein: the inner tube extends from anend of the drum proximate the gas entry zone and terminates inward of anopposite end of the drum, the length of the inner tube defining agas-solids contact zone within the drum, a solids entry zone extendingfrom a point where the inner tube terminates to the solids entry point,whereby the gas has higher velocity in the gas-solids contact zone thanin the solids entry zone.
 11. A method of coating a plurality ofparticulate solids, comprising the steps of: introducing particulatesolids into a drum having an interior wall concentric with an inner tubeso that an annular space is defined between the inner tube and the drum,a spiral element being positioned in the annular space defining a gaspathway in the annular space, the spiral element being rotatable to movesolids through the drum; applying a coating material to the particulatesolids to form coated particulate solids; rotating the spiral element tocause movement of the coated particulate solids through the drum;flowing gas from a gas entry zone along the gas pathway defined by thespiral element to dry or solidify the coating material on theparticulate solids; and discharging coated particulate solids from thedrum.
 12. The method of claim 11, wherein the inner tube is providedwith apertures and gas is flowed from the inner tube into the annularspace between the drum and the inner tube.
 13. The method of claim 11,comprising the step of applying a flowable coating material to theparticulate solids in an inlet tube having a diameter smaller than thedrum to intimately distribute the flowable coating material on theparticulate solids before the solids are introduced into the drum. 14.The method of claim 11, comprising the steps of: applying flowablecoating material that is crystallizable upon cooling to the particulatesolids, and providing the gas at a lower temperature than the coatingmaterial to solidify the coating material on the particulate solids. 15.The method of claim 11, comprising the steps of: removing gas from thedrum, conditioning the gas removed from the drum, and recycling theconditioned gas to the gas entry zone.
 16. The method of claim 11,wherein the drum is rotatable independently of the spiral element, andfurther comprising the step of rotating the inner tube with the spiralelement independently of the rotation of the rotating drum.
 17. Themethod of claim 11, comprising the step of: flowing the gas along thegas pathway countercurrently to the movement of solids in the drum. 18.The method of claim 11, comprising the step of: flowing the gas alongthe gas pathway co-currently with the movement of solids in the drum.19. A method of contacting gas and particulate solids in the manufactureof edible products, comprising: providing a drum having an interior wallconcentric with an inner tube defining an annular space between the tubeand the drum; providing a rotatable spiral element in the annular spacedefining a gas pathway; introducing particulate solids into the drum ata solids entry point; rotating the spiral element so that theparticulate solids are pushed through the drum in the annular space;flowing gas from a source of gas into the annular space between theinner tube and the drum along the gas pathway defined by the spiralelement; and discharging the particulate solids from the drum.
 20. Themethod of claim 19, comprising the steps of: removing gas from the drum,conditioning the gas removed from the drum, and recycling theconditioned gas to the annular space.